Not applicable.
Not applicable.
1. Field of the Invention
This invention relates, generally, to a composition of drilling fluids designed to decrease seepage and whole mud loss during well-working operations.
2. Description of Related Art
In the rotary drilling of wells, such as for oil and gas exploration, a mechanical means (triplex or duplex pump) of circulating drilling fluids is required in order to force the drilling fluids through a column of mechanically connected drilling pipe known as the drill string. A drilling bit or other well working tool connected to the lower end of the drill string, in combination with the mechanically induced rotating action of said drill string, drill bit, and/or other well working tool, causes the subterranean formation to be drilled.
These drilling fluids, known collectively as xe2x80x9cmudxe2x80x9d in the industry, perform specific required functions. These include, but are not limited to, (1) removing the drilled xe2x80x9ccuttingsxe2x80x9d of subterranean formation from the well bore (xe2x80x9cholexe2x80x9d); (2) controlling subsurface pressures; (3) cooling and lubricating the drill string, drill bit and/or drilling tools; (4) forming a thin and impermeable wall cake; (5) carrying information about the subterranean formations being penetrated; (6) suspending drilled cuttings and density materials when circulation is stopped; and (7) bearing a portion of the weight of the drill string through buoyancy.
These drilling fluids have a base of, but are not necessarily limited to, oil or water of varying salinity. Water-based fluids may contain, for example, bentonetic clay, polymers, materials to alter density, and other additives mixed and/or dispersed in the water. Oil-based fluids (diesel or synthetic) may contain, for example, suspending agents or materials (generally organophilic clays), wetting agents, emulsifiers, stabilizing agents, filtration agents, density agents, and other additives suspended or dispersed in diesel or synthetic oil and like oleaginous mediums.
The characteristics of the drilled geologic strata and, to some extent, the drilling apparatus, determine the physical parameters required of a drilling fluid. For example, while drilling through a high pressure subterranean formation layer, e.g., a gas formation, the density of the drilling fluids must be increased such that the hydrostatic head of the fluid column is greater than, or at balance with, the downhole pressure of the stratum to prevent gas or oil leakage into the annular space surrounding the drill string, thus lowering the chances of a xe2x80x9cblowoutxe2x80x9d situation.
The particle size in most common drilling fluids is, as a general rule, from about 0.5 to 5.0 microns in size, with a small percentage (5% or less) of the particles being as large as 44 microns (325 mesh). The particles above this range are generally removed in the process of re-conditioning and separation of the rock cuttings prior to the re-circulation of the drilling fluid. Due to the constant cleaning, conditioning and removal of larger particles, drilling fluids as they are normally used can bridge only small fissures (generally less than 0.002 inches) within the subterranean formations.
In strata that are porous in nature, having openings or fissures larger that about 0.001 to 0.002 inches, as well as having a low subterranean formation pressure, another commonly known problem exists. Some of the drilling fluid, because its hydrostatic column head pressure is greater than the subterranean formation pressure, migrates out into the porous layers rather than completing its circuit journey back to the earth""s surface.
This phenomenon makes it extremely desirable to be able to control the deposition of a low-permeability filter cake (wall cake) onto the sides of the well bore by controlling the properties of the drilling fluid. A wall cake results when the drilling fluid exerts a greater pressure than that of the subterranean formation. The initial drilling fluid that inevitably enters the subterranean formation as the wall cake is being deposited is known as spurt loss. Liquid that enter the subterranean formation after the cake has been deposited is known as drilling fluid filtrate.
If the fluids enter the subterranean formation in significant quantities, it is known as whole mud loss. This whole mud loss refers to the whole mud and includes but is not necessarily limited to, the filtrate loss and the loss of fluids in greater quantities than that considered to be fluid or seepage loss, due to such things as a fracture or vulgular subterranean formation.
In some situations, the whole mud loss may be so extreme that all well-working fluids pumped into the well bore are lost completely to subterranean sand or a vulgular formation. Such condition is known as severe or total loss to those familiar in the art.
The filtration properties required for a successful completion of a well depend on the nature of the subterranean formation being drilled and on the type of drilling fluid used. For example, in water sensitive formations, diesel or synthetic oil base drilling fluids provide superior hole stabilization when the salinity of the aqueous phase of the drilling fluid is adjusted to prevent migration of water from the drilling fluid to the subterranean formations. The filtration must be minimized through the entire drilling process, especially when using diesel or synthetic oil base drilling fluids, due to the high cost of these fluids.
Over the years, many materials have been used for in an attempt to decrease and control the filtration rate of these drilling fluids. For example, starch and starch derivatives, cellulose derivatives, humates, lignin derivatives, and various clay materials have all been used in water base drilling fluids. Similarly, asphaltic materials, organophilic clays, organophilic humates, organic lignosulfonates and the like have been used in diesel and synthetic oil base drilling fluids.
All things considered, there are very few materials effective in decreasing spurt loss or seepage of whole mud to the subterranean formation. Some of the many materials which have been used include cottonseed hulls and lentils, ground corn cobs, rice hulls, peanut shells, ground sheet mica, shells of various nuts, coal, asbestos, bagasse, paper and various particulate wood products. Accordingly, there is a need for an effective seepage and spurt control loss agent, and additionally a control agent for total and severe whole mud loss to the subterranean formation.
It is an object of the present invention to provide a well-working composition sufficient to seal fluid loss through permeable subterranean sand formations of as small as 1 Darcey to those formations that loose whole mud at a rate of approximately 100 barrels (42-gallon oilfield barrel) or more per hour.
It is another object of the present invention to provide a material additive that is capable of bridging and sealing permeable subterranean formations better than materials currently utilized for this purpose.
It is another object of the present invention to provide well-working compositions having a low seepage or spurt loss.
It is another object of this invention to provide a method of decreasing the seepage or spurt loss during a well working operation.
It is yet another object of the present invention to provide the foregoing functionality in water base, oil base, and synthetic oil base fluids.
These, and other objects of this invention will appear to one skilled in the art as the description thereof proceeds.
The novelty of this invention is a new and unique particulate material to be added to bore hole fluids, also known as well working fluids or drilling fluids, to minimize and stop whole mud loss to permeable formations encountered while drilling subterranean formations.
The particulate, ground elastomeric crumb rubber sealant material, exhibits resiliency and compressibility that differentiate it from previous and currently utilized particulate materials. Current particulate materials used for seepage and whole mud loss control applications range from the rigid inorganic minerals (i.e.; calcium carbonate, iron ore slag, mica, ground Formica, plastic, etc.) to organic materials derived from plant sources (is; cotton seed hulls, peanut hulls, corn cobs, woods, etc.).
Ground elastomeric crumb rubber sealant material exhibits the compressibility and deformability of organic materials, while maintaining rigidity after being compressed. This enables the ground elastomeric crumb rubber sealant material to bridge spaces hydraulically opened by hydrostatic pressures, yet compress and deform to close areas between the particles, sealing the void.
The ground elastomeric crumb rubber sealant material is added in quantities of about 1 ppb (pound per barrel) to 100 ppb. To ensure that the material does not adversely effect the normal properties of the particular well working fluid in use, the preferable concentration of crumb rubber material is from about 1 ppb to about 20 ppb, depending on the density of the fluid it""s added to.
The invention also relates to compositions for use in well working operations, well-working processes utilizing such compositions, and an additive to reduce the seepage loss and the total and/or severe whole mud loss of the compositions to the subterranean formations.